Increased security checks have been brought in at London Heathrow for passengers arriving from Los Angeles after 11 travellers were arrested on suspicion of smuggling cannabis over the past eight days.
Cannabis grown in California, where it is legal, commands a higher price among drug dealers in the UK, said investigators.
More than 400 kilograms of the drug were seized from 11 people who were stopped at Heathrow between January 10 and January 17.
The drugs were found in checked luggage on flights from Los Angeles to Heathrow, the National Crime Agency said.
“In light of this unusual series of seizures, law enforcement will undoubtedly be paying more attention to passengers on the Los Angeles to London route and stepping up checks," said Andy Noyes, the agency's Heathrow branch commander.
“Our investigation into these events continues but I’m making a direct appeal to anyone considering getting involved in transporting drugs to the UK. Think very carefully about the consequences.
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“Couriers who bring illicit substances in to the UK play an important role in fuelling organised crime, consequently those who are caught face stiff jail sentences. It simply isn’t worth the risk.”
Nine people have been charged with attempting to import class B drugs. The two suspects arrested on Tuesday are currently being questioned.